implementation Test() methods

clipboard.go

@@ -81,6 +81,10 @@ const (
 // guarantee one read at a time.
 var lock = sync.Mutex{}
 
+func Test() bool {
+	return test()
+}
+
 // Read returns a chunk of bytes of the clipboard data if it presents
 // in the desired format t presents. Otherwise, it returns nil.
 func Read(t Format) []byte {

clipboard_android.go

@@ -28,6 +28,10 @@ import (
 	"golang.org/x/mobile/app"
 )
 
+func test() bool {
+	return true
+}
+
 func read(t Format) (buf []byte, err error) {
 	switch t {
 	case FmtText:

clipboard_darwin.go

@@ -28,6 +28,10 @@ import (
 	"unsafe"
 )
 
+func test() bool {
+	return true
+}
+
 func read(t Format) (buf []byte, err error) {
 	var (
 		data unsafe.Pointer

clipboard_ios.go

@@ -26,6 +26,10 @@ import (
 	"unsafe"
 )
 
+func test() bool {
+	return true
+}
+
 func read(t Format) (buf []byte, err error) {
 	switch t {
 	case FmtText:

clipboard_linux.go

@@ -59,14 +59,18 @@ and initialize a virtual frame buffer:
 Then this package should be ready to use.
 `
 
-func init() {
+func test() bool {
 	ok := C.clipboard_test()
-	if ok < 0 {
-		panic(errmsg)
-	}
+	return ok == 0
 }
 
+var canAccessClipbord = false
+
 func read(t Format) (buf []byte, err error) {
+	if !canAccessClipbord && !test() {
+		panic(errmsg)
+	}
+	canAccessClipbord = true
 	switch t {
 	case FmtText:
 		return readc("UTF8_STRING")
@@ -77,6 +81,10 @@ func read(t Format) (buf []byte, err error) {
 }
 
 func readc(t string) ([]byte, error) {
+	if !canAccessClipbord && !test() {
+		panic(errmsg)
+	}
+	canAccessClipbord = true
 	ct := C.CString(t)
 	defer C.free(unsafe.Pointer(ct))
 
@@ -97,7 +105,10 @@ func readc(t string) ([]byte, error) {
 // write writes the given data to clipboard and
 // returns true if success or false if failed.
 func write(t Format, buf []byte) (<-chan struct{}, error) {
-
+	if !canAccessClipbord && !test() {
+		panic(errmsg)
+	}
+	canAccessClipbord = true
 	var s string
 	switch t {
 	case FmtText:
@@ -139,6 +150,10 @@ func write(t Format, buf []byte) (<-chan struct{}, error) {
 }
 
 func watch(ctx context.Context, t Format) <-chan []byte {
+	if !canAccessClipbord && !test() {
+		panic(errmsg)
+	}
+	canAccessClipbord = true
 	recv := make(chan []byte, 1)
 	ti := time.NewTicker(time.Second)
 	last := Read(t)

clipboard_nocgo.go

@@ -1,10 +1,14 @@
 //go:build !windows && !cgo
 // +build !windows,!cgo
 
-package clipboard
+package
 
 import "context"
 
+func test() bool {
+	panic("clipboard: cannot use when CGO_ENABLED=0")
+}
+
 func read(t Format) (buf []byte, err error) {
 	panic("clipboard: cannot use when CGO_ENABLED=0")
 }

clipboard_test.go

@@ -23,6 +23,19 @@ func init() {
 	clipboard.Debug = true
 }
 
+func TestClipboardTest(t *testing.T) {
+	if runtime.GOOS != "windows" {
+		if val, ok := os.LookupEnv("CGO_ENABLED"); ok && val == "0" {
+			t.Skip("CGO_ENABLED is set to 0")
+		}
+	}
+	t.Run("test", func(t *testing.T) {
+		if !clipboard.Test() {
+			t.Fatalf("clipboard test failed")
+		}
+	})
+}
+
 func TestClipboard(t *testing.T) {
 	if runtime.GOOS != "windows" {
 		if val, ok := os.LookupEnv("CGO_ENABLED"); ok && val == "0" {

clipboard_windows.go

@@ -27,6 +27,10 @@ import (
 	"unsafe"
 )
 
+func test() bool {
+	return true
+}
+
 // readText reads the clipboard and returns the text data if presents.
 // The caller is responsible for opening/closing the clipboard before
 // calling this function.